coloradomike

So last year I bought a cross bike for fall/winter/spring road riding (I live in the Colorado Mts and the roads can be pretty sketchy). It’s got a 40t chainring and 11-42 rear. I put some Zipps on it and 30mm gatorskin road tires. I love the geometry and the simplicity of the 1 x 11. The frame is super stiff and the disc brakes STOP on a dime. So anyway I wind up riding it all summer too! The climbing gears rock and the only thing I miss are the bigger gears for flats & descents. So my question is this - to make up for loss of the big ring should I switch to a 42t in front? or the new SRAM 10-42 in back? or do both? Thanks for any advice!

jono_

I bought a new bike this spring with the same gearing (I also have a road bike, but I found I enjoyed this cross/gravel rig more, even on the road) and I found it more than sufficient for the roads where I live, which are exclusively flats. I'm curious which bike you have, as I've thought about doing the same thing (setting it up with road tires for road rides), but that would mean investing in a new wheelset. I also had it out in the Rockies this summer and didn't really find an issue with spinning out, but likely because I don't ride descents often and was mostly enjoying them by freewheeling. With my tire setup, 40/11 at 90rpm gets you about 48 km/h and that's faster than I can keep myself going for very long on any true flat, even with a helpful tailwind.

If a bigger gear to avoid spinning out is what you're looking for, then going with the 10-42 gets you farther than just changing the chainring (40 / 10 = 4 and 42 / 11 = 3.82). Switching the cassette alone doesn't cost you anything at the other end of your gearing, which may or may not be an issue, depending on how much time you've been spending climbing in the bailout gear. My impression is that the chainring is less expensive than that particular cassette, if that's an issue.

jwalther

I'm in the same boat with my Kona Rove ST. I have a dedicated road bike, but take the Rove out occasionally and use it as my trainer bike. I've even thought about going up to a 46.

coloradomike

jono, thanks for your reply! I have a Giant TCX and I put Zipp 30 Course's on it (got em for about $800 from my local shop). In the winter I just put the original Maxxis Rambler 40m on the Zipps - which work great on everything but ice. I understand the ratios you listed so yes, the 10-42 makes more sense for me (spinning out early on descents is the issue).
Loving this bike especially on longer road rides!
What are you on?

jono_

I'm on the 2018 Giant TCX Advanced SX, which is probably what you have too if the Maxxis Rambler 40s came stock. Great bike.

ksryder

That 10-42 cassette needs a special freehub, so going to a bigger chainring is probably cheaper and simpler.

coloradomike

yep, that's the one , i have the 2017 though

shoota 

Yep, 10-42 will require a Sram XD freehub so you will need to look into if that's a possibility with your current wheels.

coloradomike

good to know, thanks!

Elvo

Be aware that the 10T cog will wear a lot quicker than most.

DrIsotope

I mean, it would, if you actually had to use it under load for any amount of time. I spend a fair amount of time in 42-10, but only going downhill at +30mph, where gravity is doing way more work than my legs. I'm a normal human, so I can't produce the +700W required to get up to 90rpm in 42/10 on the flat. I consider "spinning out" for me to be around 120rpm... which would take over 900W, and ain't never gonna happen. My last descent down the big hill (dropping almost 4,500ft in about 15 miles) I averaged 30.8mph at a stunning 83W.

The real issue with xD cassettes is that they're not especially cheap, and they're one piece-- so when you sharpen up the most-used cogs (like the 18T) you have to replace the whole thing. But I think this is more than offset by the fact that a standard 10/11 freehub + PG1130 11-42 cassette weighs about 6oz more than an xD Driver + XG1150 10-42 cassette.

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